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[79.242.63.74]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-431606c5a4bsm8047665e9.29.2024.10.17.14.47.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 17 Oct 2024 14:47:36 -0700 (PDT) Message-ID: <52bd4862-d6ce-48f6-9bc2-0f7376a56115@redhat.com> Date: Thu, 17 Oct 2024 23:47:34 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm/gup: stop leaking pinned pages in low memory conditions To: Alistair Popple Cc: John Hubbard , Andrew Morton , LKML , linux-mm@kvack.org, Shigeru Yoshida , Jason Gunthorpe , Minchan Kim , Pasha Tatashin References: <20241016202242.456953-1-jhubbard@nvidia.com> <1f8dcae1-416e-43cf-8dda-5440e0db4c00@redhat.com> <87v7xqmmxt.fsf@nvdebian.thelocal> From: David Hildenbrand Autocrypt: addr=david@redhat.com; keydata= xsFNBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABzSREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT7CwZgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63XOwU0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAHCwXwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat In-Reply-To: <87v7xqmmxt.fsf@nvdebian.thelocal> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 9F53840006 X-Stat-Signature: aa575h1pszdiffzq53bsd9hbabot1pz5 X-Rspam-User: X-HE-Tag: 1729201650-750183 X-HE-Meta: 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 LheAMnvT 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 17.10.24 23:28, Alistair Popple wrote: > > David Hildenbrand writes: > >> On 16.10.24 22:22, John Hubbard wrote: >>> If a driver tries to call any of the pin_user_pages*(FOLL_LONGTERM) >>> family of functions, and requests "too many" pages, then the call will >>> erroneously leave pages pinned. This is visible in user space as an >>> actual memory leak. >>> Repro is trivial: just make enough pin_user_pages(FOLL_LONGTERM) >>> calls >>> to exhaust memory. >>> The root cause of the problem is this sequence, within >>> __gup_longterm_locked(): >>> __get_user_pages_locked() >>> rc = check_and_migrate_movable_pages() >>> ...which gets retried in a loop. The loop error handling is >>> incomplete, >>> clearly due to a somewhat unusual and complicated tri-state error API. >>> But anyway, if -ENOMEM, or in fact, any unexpected error is returned >>> from check_and_migrate_movable_pages(), then __gup_longterm_locked() >>> happily returns the error, while leaving the pages pinned. >>> In the failed case, which is an app that requests (via a device >>> driver) >>> 30720000000 bytes to be pinned, and then exits, I see this: >>> $ grep foll /proc/vmstat >>> nr_foll_pin_acquired 7502048 >>> nr_foll_pin_released 2048 >>> And after applying this patch, it returns to balanced pins: >>> $ grep foll /proc/vmstat >>> nr_foll_pin_acquired 7502048 >>> nr_foll_pin_released 7502048 >>> Fix this by unpinning the pages that __get_user_pages_locked() has >>> pinned, in such error cases. >>> Fixes: 24a95998e9ba ("mm/gup.c: simplify and fix >>> check_and_migrate_movable_pages() return codes") >>> Cc: Alistair Popple >>> Cc: Shigeru Yoshida >>> Cc: David Hildenbrand >>> Cc: Jason Gunthorpe >>> Cc: Minchan Kim >>> Cc: Pasha Tatashin >>> Signed-off-by: John Hubbard >>> --- >>> mm/gup.c | 11 +++++++++++ >>> 1 file changed, 11 insertions(+) >>> diff --git a/mm/gup.c b/mm/gup.c >>> index a82890b46a36..24acf53c8294 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -2492,6 +2492,17 @@ static long __gup_longterm_locked(struct mm_struct *mm, >>> /* FOLL_LONGTERM implies FOLL_PIN */ >>> rc = check_and_migrate_movable_pages(nr_pinned_pages, pages); >>> + >>> + /* >>> + * The __get_user_pages_locked() call happens before we know >>> + * that whether it's possible to successfully complete the whole >>> + * operation. To compensate for this, if we get an unexpected >>> + * error (such as -ENOMEM) then we must unpin everything, before >>> + * erroring out. >>> + */ >>> + if (rc != -EAGAIN && rc != 0) >>> + unpin_user_pages(pages, nr_pinned_pages); >>> + >>> } while (rc == -EAGAIN); >> >> Wouldn't it be cleaner to simply have here after the loop (possibly >> even after the memalloc_pin_restore()) >> >> if (rc) >> unpin_user_pages(pages, nr_pinned_pages); >> >> But maybe I am missing something. > > I initially thought the same thing but I'm not sure it is > correct. Consider what happens when __get_user_pages_locked() fails > earlier in the loop. In this case it will have bailed out of the loop > with rc <= 0 but we shouldn't call unpin_user_pages(). Ah, I see what you mean, I primarily only stared at the diff. We should likely avoid using nr_pinned_pages as a temporary variable that can hold an error value. -- Cheers, David / dhildenb